1. Field of the Invention
The invention relates to a method for reducing the polygon effect that occurs during the course of the reversing of a chain, which can be used for a pedestrian conveyor, in particular an escalator or moving walkway.
2. Related Art
German Patent Document DE-A 199 58 709 describes a method and a device for reducing the polygon effect in the reversing area of pedestrian conveyors.
The polygon effect is caused by the polygonal rest of the chain on the chain wheel. With increasing rotation angle, the effective radius of the chain wheel varies, whereby the velocity of the chain oscillates between a maximum and a minimum value. When engaging the chain wheel, the chain rolls and the teeth of the chain wheel have different velocities, which cause impacts. The revolution effect is caused by the angular momentum which is transmitted from the chain wheel onto the chain links and thus onto the steps or pallets. After the chain has run out of the chain wheel, this angular momentum is temporarily maintained due to the inertia of the system, which leads to the so-called curling of the chain. The angular momentum is reduced by friction in the chain respectively by impacts between chain and guiding if a chain guiding element is provided. In contrast to the modifications that have been known so far and which have been exclusively provided in the mechanical field, DE-A 199 58 709 presents a concept, which contains an electrical solution, namely a modification of the drive.
German Patent document DE-A 100 20 787 describes an operational controlling apparatus of an escalator, comprising a frequency converter for converting a three-phase alternating mains current into an alternating current having a variable voltage and a variable frequency, in order to control the operational speed of the escalator; a gear and a chain wheel for driving a tread plate using a rotation force, which is generated by an induction motor, and a current detector for detecting a current, which flows within the induction motor, a controlling apparatus for an escalator comprising: a speed detector for detecting the rotation speed of the induction motor; a position detector for detecting the rotation position of the chain wheel; and a controlling device, which controls the frequency converter by means of an output signal of the speed detector and the position detector for obtaining a current, which compensates the vibrational angular momentum, wherein the above current is added to a current output by a speed controlling apparatus; wherein an actual current detection value of the induction motor is subtracted from the resulting current value; and wherein a pulse duration modulation signal is generated accordingly.